Lubricant containing copolymer viscosity index improver



United States Patent 2,994,663 I LUBRICANT CONTAINING COPOLYMER VISCOSITY INDEX IMPROVER Warren .Lowe, San Francisco, and Frank A. Stuart,

Orinda, Califl, assignors to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Filed Aug. 10, 1959, Ser. No. 832,493

5 Claims. (Cl. 252-56) This invention relates to a superior new lubricant composition. More particularly, the invention is concerned with a novel polymer thickened lubricant composition having an improved viscosity index.

Lubricant compositions in many present-day applications contain viscosity index improvers in order to be more etfective over a wide temperature range. At low temperatures such as normal starting temperatures of internal combustion engines, the lubricant compositions must be sufiiciently fluid to circulate freely and provide a lubricating film between wearing surfaces such as bearings, piston rings, and cylinder walls. 0n the other hand, at high temperatures like the usual operating temperatures of internal combustion engines, the lubricant composition should be thick enough to give a similarly protective lubricating film. I

It has now been found thatsurprisingly improved viscosity indexes are provided in a lubricant composition comprising a major proportion of an oil of lubricating viscosity and a minor proportion, sufiicient to improve the viscosity index of said oil of the copolymer of (A) vinyl alkyl ether having from 2 to 6 carbon atoms in the alkyl group and (B) at least one ester of the class consisting of alkyl acrylates and alkyl methacrylates having from 4 to 12 carbon atoms in each of the alkyl groups, the total of carbon atoms in the'alkyl "group of (A) and the average alkyl group of (B) being from about 8 to about 12, the mol ratio of (A) to (B) being-approximately 1:1 and the molecular weight of the copolymer being at least 50,000.

The lubricant composition of the invention containing the particular copolymer'described above possesses an unusually high viscosity index compared to other lubricant compositions containing viscosity. index improvers as previously suggested in the art. .The particularbalance of. the carbon atoms in theialkyl groupsfof the copolymer of the lubricant composition as well as the ratio of monomers and the minimum molecular weight are all critical ice polymer, the ratio of w to x +y being approximately 1:1 and the total carbon atoms of wR; and xRg-i-yR being from about 8 to about 12.

Suitable unsaturated alkyl ethers the above description include vinyl isobutyl ether, vinyl n-butyl ether, vinyl Z-ethylhexyl ether, etc. For present purposes the -vinyl alkyl ethers having 4 to 6 carbon atoms in the alkyl group are preferred.

Alkyl esters of methacrylic acid and acrylic acidin accordance with the above formula include n-octyl methacrylate, n-octadecyl acrylate, Z-ethylhexyl acrylate, Oxy decyl methacrylate, n-butyl methacrylate, etc. The alkyl methacrylates having 4 to 12 carbon atoms in the alkyl groups are presently preferred. H I

The copolymers are prepared by conventional bulk, solution or emulsion methods, in the presence of an addition-type polymerization initiator. Preferably, the copolymerization is effected in an inert organic solvent,- such as benzene, toluene, xylene or petroleum naphtha, in the presence of a free radical-liberating type initiator such as a peroxy compound, for example, benzoyl peroxide, acetyl peroxide, tert. butyl hydroperoxide, ditert. butyl peroxide, dibenzoyl peroxide, or di-tert. amyl peroxide, or an azo initiator such as 1,1-azodicyclohexanecarbonitrile or a,a'-azodiisobutyronitrile, or a persulfate, such as potassium persulfate. The catalyst, or polymerization initiator, is employed in an amount of from about 0.1 to 10%, with a preferred range being from 0.10 to 2%. If desired, the catalyst can be added in increments as the reaction proceeds. Likewise, additional portions of the solvent can also be added from time to time in order to maintain the solution ina homogeneous condition. The temperature of copolymeri: zation varies from about 100 to 300 F., with the optimum temperature for any given preparation depending on the nature of the solvent, the concentration of monomers present in the solvent, the catalyst, and the duration of the reaction. Much the same conditions are employed when the copolymerization is effected in bulk rather than in the presence of an inert solvent.

The copolymers have molecular weights of at least about 50,000, as already mentioned. The molecular to the provision of viscosity index improved lubricant compositions of this unusual quality. Other, closely related copolymers of the vinyl alkyl ether type in lubricant compositions are remarkably less satisfactory by comparison. I

ing to the invention have in which R is'an alkyl group of from 2 to 6 carbon atoms and R and R are alkyl groups of from 4 to 12 carbon atoms each, :all of which may be the same or difierent I from one another, R4 and R are members of the class consisting of hydrogen and methyl groups, and w,-x, and i y beingthe relative occurrence of the (A) and (B) mono mer units, asdescribed above, in which relationship w is equal to l while'x' and y are fractional numbers, the E sum of which isequal to l, the total occurrenceof the monomerunits in the formula beingieguivalent to a molecular weight of at least -50,000f or the total 'coring at 140 F. for 2 hours; the lower lilyl is decau t;e an i o'm ist idfwaeri qdeaio l q ea fi u weight may run as high as several millionor more. Polymers having molecular weights of from about 200,000 to about 1,000,000 are preferred. The aforementioned molecular weights are based on standard viscosity determinations. V The following specific example illustrates the preparation of the copolymer of vinyl isobutyl ether, n-butyl acrylate and n-octyl acrylate.

Into a 2-liter, B-necked flask equipped with water condenser, addition funnel, thermometer, stirring unitand heating means, is charged 9 grams of sodium lauryl sulfate and 420 ml. of distilled water. After 'stirringat' temperature for 1% hours, 1% grams of"sodium-pyro-.

phosphate, l /zlgrams of potassium persulfate,.iandi 35.01 cc. vinyl isobutyl ether are added with stirring. Stirring: is continued for l /z hours and .from an' addition funnel a mixture is slowly introduced containing 135 grams polymerization inhibitor-free noctyl acrylate and 32 grams} of inhibitor-free n-butyl acrylate. The time of addition, is 1% hours. Temperature of the reaction mixture during reaction is to F. e i

V1 The total mixture is vigorously stirred at' 150 tb l60 f i F. for 4 hours. Aftr'heating slowly-to 170 R, an ex othermic reaction takes place. A cold water bath is user to cool the reaction mixture. The thickened mixture'is stirred at to F. for 4 hours. .The resulting pol mer is coagulated by the'addition. of 20'grams of drated aluminumsulfate, Al (SO -.1 8H 0. After sti flask and stirring is continued for 2 hours at 140 F. The polymer is dissolved in 300 ml. of benzene and reprecipitated with 750 ml. of methanol. The solvents are removed from the reaction mixture by distillation un- While satisfactory lubricant compositions can be obtained by adding to the base oil employed only one or more of the polymeric additives of the type described above, it also falls within the purview of this invention der'r'educed pressure. The copolymer product obtained 5 to provide lubricant compositions which contain not only after the removal of the solvents isthe ternary copolymer such polymers, but also other additives such as oiliness and of vinyl isobutyl ether, n-butyl acrylate and n-octyl extreme pressure agents, anti-oxidants, corrosion inhibiting aerylate having a mole ratio of 1 to 0.25 to 0.75. The agents, blooming agents, the temperature-viscosity charc'opolymer has a molecular weight of approximately acteristics of the oil. The present invention also contem- 200,000. plates the addition to the lubricant composition (partic- -In general, excellent viscosity indexes can be imparted ularly when the amount of copolytner employed is relat'o lubricating oils by dissolving in them a quantity of from tively small) of detergents and/ or anti-wear agents. about 0.1 to 10% by weight of the polymers of the type Illustrative lubricant compositions of the above type described above, although a preferredrange is from about containing the copolymeric additives of the invention in l to 5% weight. On the other hand, since the polymers combination with other agents may include, for example, of this invention are unusually compatible with mineral from about 0.1 to 10% by weight of alkaline earth metal and other lubricating oils in substantially all proportions, higher alkylphenate and sulfonate detergents, such as as much as 75% of the present polymeric additives can calcium alkylphenates having an average of approximatebe dissolved in a suitable lubricating oil for the purpose 1y 14 carbon atoms in the alkyl group and basic calcium of preparing a concentrate capable of dilution with petroleum sulfonate, as Well as organic thiophosphate corlubricating oils and the like to prepare the final lubricant rosion and high temperature oxidation inhibitors such as composition. Such concentrates, which may also conthe reaction product of pinene and P 8 and the bitain other additives in desired amounts, and which norvalent metal dihydrocarbyl dithiophosphates, zinc butyl mally contain at least 10% of the polymer, comprise a hexyl dithiophosphate and zinc tetradecylphenyl dithioconvenient method for handling the polymer and may be phosphate in amounts of irom about 0.1 to 10% by weight used as a compounding agentfor lubricants in general. of the composition.

The polymeric additives of this invention can be used The efiicacy of polymericadditives of the type described with good effect in the case of any one of a wide variety above as viscosity index improving agents in lubricating of oils of lubricating viscosity, or of blends of such oils. Oils is illustrated y d from a number 0f tests- Various Thus, the base oil can b a refined Pennsylvania o other amounts of the polymeric additives are incorporated in the paraflin base oil, a refined naphthenic base oil, or a synoil as noted in the following table in terms of percent thetic hydrocarbon or nonhydrocarbon oil of lubricating y Weightviscosity. As synthetic oils there can be alkylated waxes l lfi is a solvent refined mineral lubric Oil base and similar alkylated hydrocarbons of relatively high comamlng 45 mlllimoles P kilogram of basic Calcium molecular weight, hydrogenated polymers of hydrocar- PFtTOIeUm $111f0I1ate, 10 millimoles per kilogram of zinc bons, and the condensation products of chlorinated alkyl d1 (aJkYlPhenY1) dlthlophosphilte by Weight of hydrocarbons with aryl compounds. Other suitable oils filparaffin polysulfide' The lvlswslty, of 011 A at are those which are obtained by polymerization of lower 13 (saifbolt Seconds Upiversal) e molecular weight alkylene oxides such as propylene 40 2 at 1 is 4507 glvmg a Vlscoslty Index and/or ethylene oxide. Still other synthetic oils are ob- O B t fined a1 1 b tained by 'etherification and/or esterification of the hya a. im-mer u rwatm-g 011 5 tammg 40 mrllnnoles per kilogram of basic calium droxy groups in alkylene oxide polymers such as, for petroleum sulfonate 6 minimal er f example, the acetate of the Z-ethylhexanol-ifiitiated polydi(a1ky1pheny1) diflgl-ophdsphate k g g -i 3 2 11 m 2 Qther Imports-1199195865 f Y parafiin polysulflde and 0.001% by weight of silicone 2 31 m 1 1 b e ffl s esters Pf foam mlnbitor. The base oil has a viscosity index or 96. l Y' Y Se acate, tflcfesll p pl i and slllcate 011 C 1s a typical 140 neutral mineral lubricating oil. esters such as hexa (Z-ethyl butoxy) disiloxane. If de- The bas oil has a viseo ityindex of 90. s red, the 011 can be a mixture of mineral and synthetic Oil D is a typical 150 neutral mineral lubricating oil. oils. 50 The base oil has a viscosity of 90.

Table T t 1 I V No. 'zRr-l- Poly- (Thon- F 210 F.

yRa mer sands) H 1 0.25 0.75 11 A: 3.75" 385 '4 1- H 1 0.75 0.25 9 A 3.75 250v 233.2 ig i2? H 1 0.75 0.25 9 A 4 455 251.9 88.9 154 H Y 1 0.75 0.25 9 B 2 175 v191.4 54.8 158 H 1 0.75 0.25 9 B 3- 230 210.9 53.27 155 H 1 0.75 0. 25 9 B 4 265 226.9 72.47 157 H 1 0.75 o. 25 9 0 4* 300 203.5 71.11 170 CH; 1 0.5 0.5 15 B 2 70 215.5 50.33 CH3 1 0.75 o. 25 11.5 B 2 80- 203.1 50.55 CH; 1 0.5 0.5 17 B 2 60 213.2 49.75 124. CH; 1 05 v 0.5 18 .B 2 80. 219.6' 50.45 125 1 1 12 B 1 2 l 244. 5 1 r 1 12. B m 2 5140 245.; i i 1 1, 12, B. 2 .175 n 259 54.29 I 131 H 1 0. 5 10 E 4 313.5 385:92 142 H 1 0.25 11 A 4v 3 285 437.4 74.32 136 1 I 1 12 o. 4- 480 507 85.83 140. H 1 0.5 I 10 o 4- 269 318.4 57.85 147- 1 1: --10 13 :2 .325, :3041" 6414: H 1 .25 0.75. .9 A. ,4 .310 326.8 76.39.. 154: H 1 0.4 0.5 9. 5 A; -54 395 434.7, 83.81 145 H 1 0.25 0.75 9.5 a ;4. j295" 297.7. 74.34. .157- l r i2 a 52 3 a r a s.- 1 1 12 14 3.75 350 452.5 711 i g,

From the tests in the foregoing table, it will be seen that each of the illustrative compositions containing the copolymeric thickeners according to the invention possesses surprisingly improved viscosity-temperature properties compared to base oils alone. Furthermore, the particular copolymers of vinyl 'alkyl ethers and alkyl methacrylates having the appropriate balance of carbon atoms in the alkyl groups are much superior to other closely related copolymers without this proper balance.

The above results are even more surprising when compared to viscosity indexes obtained with homopolymers of either vinyl alkyl ether or alkyl acrylates or alkyl methacrylates alone. Although the viscosity index obtained with the alkyl esters in similar compositions is about 140 and that with vinyl ether is about 130, the viscosity index with the preferred coplymers oi the invention is as high as 170, which is surprisingly better than would be expected from the average of the two We claim:

1. A lubricant composition comprising a major proportion of an oil of lubricating viscosity and a minor proportion suflicient to improve the viscosity index of said oil of the copolymer of (A) vinyl alkyl ether having from 2 to 6 carbon atoms in the alkyl group and (B) at least one ester of the class consisting of alkyl acrylates and alkyl methacrylates having firom 4 to 12 carbon atoms in each of the alkyl groups, the total of carbon atoms in the alkyl group of the (A) and the average alkyl group of the (B) monomers being from about 8 to about 12, the mol ratio of (A) to (B) being approximately 1:1 and the molecular weight of the copolymer being at least about 50,000.

2. A lubricant composition comprising -a major proportion of mineral lubricating oil and a minor proportion sufiicient to improve the viscosity index of said oil of the copolymer of (A) vinylisobutyl ether and (B) a mixture of n-butylacrylate and n-octylarcrylate, the mol ratio of (A) to (B) being approximately 1:1 and the molecular weight of the copolymer being at least about 50,000.

3. A lubricant composition comprising a major proportion of mineral lubricating oil and a minor proportion sufficient to improve the viscosity index of said oil of the copolymer of (A) vinyl 2-ethylhexyl ether and (B) n-butylacrylate, the mol ratio of (A) to (B) being approximately 1:1 and the molecular weight of the copolymer being at least about 50,000.

10 4. A lubricant composition comprising a major proportion of mineral lubricating oil and a minor proportion sufiicient to improve the viscosity index ct said oil of the copolymer of (A) vinyl n butyl ether and (B) a mixture of n-butylacrylate and n-octylacrylate, the mol ratio of (A) to (B) being approximately 1:1 and the molecular weight of the coplymer being at least about 50,000.

5. A concentrate for the preparation of lubricant compositions comprising from 25 to 90 percent by Weight of mineral lubricating oil and from 10 to 75 percent by weight of the copolymer of (A) vinyl alkyl ether having from 2 to 6 carbon atoms in the alkyl group and (B) at least one ester of the class consisting of alkyl acrylates and alkyl methacrylates having from 4 to 12 carbon atoms in each of the alkyl groups, the total or canbon atoms in the alkyl group of the (A) and the average alkyl group of the (B) monomers being from about 8 to about 12, the mol ratio of (A) to (B) being approximately 1:1 and the molecular weight of the copolymer being at least about 50,000.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A LUBRICANT COMPOSITION COMPRISING A MAJOR PROPORTION OF AN OIL OF LUBRICATING VISCOSITY AND A MINOR PROPORTION SUFFICIENT TO IMPROVE THE VISCOSITY INDEX OF SAID OIL OF THE COPOLYMER OF (A) VINYL ALKYL ETHER HAVING FROM 2 TO 6 CARBON ATOMS IN THE ALKYL GROUP AND (B) AT LEAST ONE ESTER OF THE CLASS CONSISTING OF ALKYL ACRYLATES AND ALKYL METHACRYLATES HAVING FROM 4 TO 12 CARBON ATOMS IN EACH OF THE ALKYL GROUPS, THE TOTAL OF CARBON ATOMS IN THE ALKYL GROUP OF THE (A) AND THE AVERAGE ALKYL GROUP OF THE (B) MONOMERS BEING FROM ABOUT 8 TO ABOUT 12, THE MOL RATIO FO (A) TO (B) BEING APPROXIMATELY 1:1 AND THE MOLECULAR WEIGHT OF THE COPOLYMER BEING AT LEAST ABOUT 50,000. 